The subject matter of this disclosure is a novel arc discharge lamp which may be used in a variety of lighting applications. The invention has been prompted, however, by a quest for an improved arc discharge light source which may be employed in a rotating beacon of a navigational signal.
The principal object of a navigational signal light is to emit as much light flux as possible from a reliable light source and direct the light into the plane of the horizon. The light may be radiated in all horizontal directions simultaneously, or it may be collected into one or more narrow beams which are mechanically rotated. There are basically two types of devices producing rotating beams or beacons. In the first type, a rotating screen surrounds a stationary lamp. The screen contains multiple lenses or other means for concentrating light. The rotating screen generally produces multiple beams, one beam associated with each lens or sector subtended by a lens. The emitted light within any sector is formed into a pencil beam and swept only within that sector. For an example of this type of beacon and a metal-halide arc discharge lamp having uniform azimuthal intensity for use therewith, see U.S. Pat. Application, Ser. No. 909,359, referred to above.
In the second type of rotating beacon device, a reflector or other means of concentrating the light is employed with the lamp. The entire optical system, i.e., lens and reflector, is rotated. This method generally produces a single beam; all of the emitted light is swept through 360 degrees repeatedly. It is this type of rotating beacon and, more particularly, the light source associated therewith, which is the subject of this disclosure.
Although filament lamps have been heavily relied on in the past for navigational signal lighting, modern light sources, more particularly arc discharge sources, will undoubtedly be employed in increasing numbers in the future because of the many advantages offered by these light sources. An arc discharge lamp generally provides better efficacy and longer life than its incandescent counterpart. The electrodes are heavier than the filament, so that the lamp may be more rugged. In an arc discharge lamp, the length and width of the arc are design variables to a large extent. In an incandescent lamp, the length and width of the filament are for the most part determined by the lamp wattage. Thus, there is greater flexibility in the choice of optical characteristics of the light source with arc discharge lamps than with comparable incandescent lamps. This is a significant factor in signal lighting, particularly with lamps of three hundred watts or less.
Xenon compact source and linear xenon lamps have been employed as light sources in lighthouses. See Lamps and Lighting, Third Edition, edited by Cayless and Marsden, on Page 259, published by The Pitman Press, Bath, Great Britain. In the Illuminating Engineering Society of North America's Lighting Handbook. 1981, Reference Volume, in FIG. 8-59(b) on Page 8-51, there is shown a twenty kilowatt xenon compact arc source with liquid cooled electrodes. This light source typically is employed in military searchlights where the principal operating position of the lamp is horizontal. More generally, see United States Coast Guard, Ocean Engineering Report No. 37 (CG-250-37) Visual Sionallinc: Theory and Application to Aids to Navigation, 1970.
In U.S. Pat. No. 4,498,027, issued Feb. 5, 1985, to Karlotski et al., there is disclosed a double-enveloped arc discharge lamp for horizontal operation having a line-of-sight arched arc tube to accommodate the upward bowing of the arc discharge during steady state operation of the lamp. The lower wall of the arch has lesser curvature than the upper wall to accommodate the position of the arc discharge during lamp start and warm-up when the arc tube is cooler and the arc is arched to a lesser degree. The arc tube is mounted within the outer envelope with the central axis of the arc tube substantially parallel to the central axis of the outer envelope. See also, U.S. Pat. No. 3,858,078, issued Dec. 31, 1974, to Koury; A New Generation of Metal-Halide Lamps, by Koury, Gungle, and Waymouth, Journal of the Illuminating Engineering Society, January 1975; and U.S. Pat. No. 4,056,751, issued Nov. 1, 1977, to Gungle et al.
In U.S. Pat. No. 2,218,013, issued Oct. 15, 1940, to Tice et al., there is shown an aviation beacon light having an elongated body which appears to be orthogonal to the stand or base (although the body rotates with respect to the stand).
It would be an advancement of the art if an arc discharge lamp could be provided which may be used for a variety of lighting applications and is well suited for navigational signal applications.